Data services developed for public mobile networks with extensive coverage areas and supporting the mobility of the user have evolved significantly in recent years. The packet switched General Packet Radio Service (GPRS) provides the GSM networks with efficient data transmission, where radio capacity is allocated only during packet transmission. The third generation mobile communications system standardized by the Third Generation Partnership Project (3GPP), also referred to as the 3GPP system or the UMTS system (Universal Mobile Telecommunications System) offers more enhanced data transmission services than the GSM/GPRS networks.
In addition to the data services offered by the PLMN networks, various wireless local networks have been developed that offer a broadband wireless data transmission service for a limited coverage area. The IEEE 802.11-based WLAN networks represent examples of such techniques. Such local networks can be used in different hot spots, such as offices or airports, to offer extremely fast data transmission and access to the Internet. Wireless local area networks and PLMN networks have also been converged. For instance, network elements have also been designed for wireless local area networks that allow the local network to utilize the PLMN network. Network elements have been created for the WLAN networks according to the IEEE 802.11 standard and GSM networks that allow access to the authentication and billing services offered by the GSM network through the WLAN network. The co-operation between PLMN networks and wireless local area networks has been planned further so that the services offered by the PLMN network could also be used through a radio interface offered by the wireless local area networks. In the 3GPP system the wireless local area network might operate as an access sub-system.
In Mobile IP environment it is possible that a mobile node (MN) has two or more different links for data transfer. As mobile devices may move between access networks having very different capabilities, ongoing data transfer may suffer from such transition, especially when the mobile device is moving from a network offering a connection with large data transmission capacity, for instance a WLAN, to a network providing substantially lower data transmission capacity, such as a GPRS network. For instance, a WWW browser of a mobile device has a TCP session with a WWW server and downloads files via this TCP session. If the connection is arranged via WLAN, and suddenly the mobile device moves out of the WLAN coverage, the mobile device must start to use GPRS to continue the TCP session. Because the data transfer rate offered by the GPRS network is slower than that of the WLAN, many packets may be lost and thus many TCP retransmissions need to be executed before TCP congestion control handles this problem.
US 2002/0141353 aims to improve data throughput in the case of a transmission channel switch, where a newly assigned channel has a smaller transmission rate. If a forthcoming channel switch is detected, transmission parameters of the old channel are adapted on the basis of the new channel. For instance, the data transmission rate of the old channel is reduced before the channel switch, whereby it is possible to at least reduce the problems caused by the change to a slower channel. An example of a UMTS channel switch is described, wherein an RRM unit signalizes the channel switch to a MAC unit in order to change the channel parameters.